Text Executive Programming Language

From Seo Wiki - Search Engine Optimization and Programming Languages

In 1979, Honeywell Information Systems announced a new programming language for their time-sharing service named TEX, an acronym for the Text Executive processor. TEX was a first generation scripting language, developed around the time of AWK and used by Honeywell initially as an in-house system test automation tool.

TEX extended the Honeywell Time-Sharing service (TSS) line editor with programmable capabilities which allowed the user greater latitude in developing ease-of-use editing extensions as well as write scripts to automate many other time-sharing tasks formerly done by more complex TSS FORTRAN programs.

Overview

TEX was a subsystem of Honeywell TSS. Users would enter the TSS command 'tex' to change to a TEX session mode of operation. TEX expressions could be entered directly on the command line or run from script file via the TEX command CALL <filename>.

TEX programs are a collection of TSS line editing commands, TSS session commands and TEX statements. TEX variables could be inserted into TSS commands and TSS line editor commands via the TEX variable substitution feature. TEX programs were primarily designed to extend the line editor system. Consequently, TEX had no concept of file input/output relying instead on applying line edit commands to the working file and saving as needed.

The key developers of TEX at Honeywell were Eric Clamons and Richard Keys with Robert Bemer, famous as the father of ASCII and grandfather of COBOL, acting in an advisory capacity.[1]

TEX should not be confused with TeX a typesetting markup language invented by Donald Knuth.

Variables

All variables were stored as strings and converted to integer numeric values when required. Floating
point variables, arrays or other datatypes common in current scripting languages did not exist in a TEX environment.

All variables were stored in a single global variable pool which users had to manage in order to avoid
variable naming conflicts. There were no variable scoping capabilities in TEX. Variable names were limited to 40 characters.

TEX provided several internal read-only registers called star functions or star variables which changed state when certain TEX string parsing operations were executed. Star functions provided a means to get the current date and time, resultant strings from a split or scan string parsing operations, TEX internal call level and TSS session information.

The maximum length of a string value was 240 ASCII characters. This includes intermediate results when evaluating a TEX expression. Numeric string values are limited to 62 digits in the string including the (-) for negative numbers. Numeric values are also normalized where leading zeros are stripped from the string representation.

Some examples of variable usage:

_ we can use quotes or other characters as delimiters as long as the string doesn't contain them
a="hello"
_ here we use the / character as a delimiter (a common practice especially if the string has a " char)
b=/world/

_ the out statement will print "hello world" to the terminal without the quotes
out:c

_ here we use a TEX variable in a line editing command to find a line starting with "hello world"
hello="hello world"
f:hello

_ here we are replacing the "hello" string with the "hello world" string
rs:a:c

Operators

TEX has three types of operators:

arithmetic

boolean

string

When constructing a TEX expression, all spaces must be compressed out except for string literals. In general,spaces
delimit TEX statements.

_ in the "d=" statement there are no spaces between the commas or the variables
a="hello" b=" " c="world" d=a,b,c out:d

_ the space separates the 'if' from the expression and the expression from the next TEX command to conditionally execute
if a:eqs:"hello" out:a

Arithmetic

TEX supports only basic integer arithmetic operations:

unary sign number prefix (+/-)

addition (+),

subtraction (-),

multiplication (*) and

division (/)

with up to 16 levels of parentheses.

Some examples are:

a=1
b=-2
c=3*(a-b)/(2*2+(4+1))

Boolean operators

TEX boolean operators come in two flavors for:

numeric comparisons

string comparisons

They were most often used within the context of an IF control statement.

A list of available numeric boolean operators in TEX are:

:eq: or :eqn: returns t for true if two values are numerically equal

:ge: or :gen: returns t for true if first value is numerically equal to or greater than second value

:le: or :len: returns t for true if first value is numerically equal to or lesser than second value

:gt: or :gtn: returns t for true if first value is numerically greater than second value

:lt: or :ltn: returns t for true if first value is numerically lesser than second value

:ne: or :nen: returns t for true if first value is not numerically equal to the second value

A list of available string boolean operators are:

:eqs: returns t for true if two strings values are identical in characters, case and length

:ges: returns t for true if first string is greater than or equal to the second string in characters case and length

:les: returns t for true if first string is less than or equal to the second string in characters case and length

:gts: returns t for true if first string is greater than or equal to the second string in characters case and length

:lts: returns t for true if first string is less than to the second string in characters case and length

:nes: returns t for true if first string is NOT equal to the second string in characters case and length

String boolean operators are affected by the TEXCASE mode. Under CASE mode, strings such as 'ABC' and 'abc' were considered equal (TEX converted 'ABC' to 'abc' prior to the comparison). Under NOCASE mode, the 'abc' string would be considered greater than the 'ABC' string based on the ASCII code point value for 'a' being a larger value than the 'A' ASCII code point value.

The boolean NOT operator was represented by the circumflex character (^).

Some examples of boolean operators in action:

if name:eqs:"luke" out:"May the force be with you!"
if ^age:gtn:500 out:"Heh, you can't be Yoda!"

TEX did not provide and or or connecters to make more complex boolean expressions. Instead, programmers had to use nested if statements for and connections and a block of if...do something statements to handle or connections:

_ an example of an and construct
if a:eqs:'a' if b:eqs:'b' goto !its_true
goto !its_false

scanning a string from the left for a given substring and saving the left side ('>)

scanning a string from the left for a given substring and saving the right side (>')

scanning a string from the right for a given substring and saving the left side ('<)

scanning a string from the right for a given substring and saving the right side (<')

Some string scanning/parsing examples:

a="hello world"
b=a'>" "
out:b

Labels

All TEX statement labels were prefixed with a (!). Statement labels were in general ignored unless referenced by a goto or call statement. One noteable feature of TEX was the ability to call or goto labels in other files. Coupled with the TEXSUBS mode meant that TEX could create new scripts via line editing, save and then call or goto labels in these scripts dynamically.

In the above example, TEX would process the /mycat/mypgm file searching for the !hello label(*). TEX would continue processing the file until a return statement or exit statement was executed or end of file was reached.

Goto by label example:

goto /mycat/mypgm!hello2

In the next example, TEX would process the /mycat/mypgm file searching for the !hello2 label(*). TEX would continue processing until an exit statement or end of file was reached. An error would be thrown if a return statement was executed and there were no CALLs active.

(*) TEX did not check for duplicate labels in the same file, consequently execution was unpredictable if present.

Substitutions

TEX provides the SUBS and NOSUBS commands to activate or deactivate variable substitution for subsequent TEX statements or TSS commands.

xx=/out:"Hello World"/
subs ?
?xx?
nosubs
?xx?

In the above example, the xx variable contains a TEX output statement as its value. The subs command specifies that (?) is the substitution character for all future statements of the program. Upon processing the first ?xx? line, TEX will substitute in the out:"Hello World" command for ?xx? and then execute the resultant statement. The nosubs command turns off substitutions for subsequent statements and so TEX issues an error when it tries to execute the second ?xx? line.

Indirections

In addition to variable substitution, TEX supported variable indirection. Variables prefixed with the underscore character (_) were considered to contain a variable name as their contents and so TEX would use indirection to get the value. TEX limited indirection to 64 levels to avoid possible looping.

As an example:

a="b"
b="c"
c="hello world"
_ here the out would print "hello world" to the terminal,
_ since __a == _b == c and so the command became out:c.
out:__a

Input/output

Honeywell Timesharing sessions had a concept of the working file. To edit an existing file, you would first make it the working file via the old command. To create a new file, you would first create it via the new command. Once changes were complete, you would either save (for new files) or resave the working file. Basically only one file could be open for editing at a time.

TEX programs were primarily designed to extend the line editor system. Consequently, TEX had no concept of file input/output relying instead on making changes to the working file via line edit commands and saving as needed.

However, TEX did provide terminal-oriented input/output commands:

in -- print a prompt and pause until text is entered, storing it in the *in star variable

out -- print a message

A simple example using in and out:

in:"What is your name?"
out:"Hi ",*in

Star variables and functions

TEX provided star variables as a means to access results or side-effects of TEX system functions or to represent ASCII terminal codes.

A list of star variables follows:

*account - user account number associated with the current userid

*cl - the current line of the current file being edited

*lcl - the length of the *cl value

*clvl - current depth of calls

*date - current date in the form of YY-MM-DD

*eof - T if positioned after the last line of the current file or when there is no current file

*in - contains the last response to an in or intTEX command execution

*lin - length of *in

*left or *l - left string from scan or split command execution

*lleft or *ll - length of *left

*middle or *m - middle string from scan or split command execution

*lmiddle or *lm - length of *middle'

*right or *r - right string from scan or split command execution

*lright or *lr - length of *right

*null - represents the null string

*random - contains a randomly selected digit from 0 to 9

*rmdr - remainder of the last division operation

*snumb - system number of the last batch job run

*svmd' - TEX commands to restore the TEX modes at the time of the last interfile call or goto

Edit Commands

The <search_expression> could contain a range as in F:/hello/,/world/ to find all lines that start with the string "hello" and contain the string "world" too.

TEX provided standard line-based file editing commands:

P: print current line

F: move forward thru the current file line by line

B: move backward thru the current file line by line

A: append after the current line

I: insert before the current line

R: replace the current with the expression provided

D: delete the current line

copy: copy the current line

cut: copy and delete the current line

paste: paste what was cut or copied before the current line

Each command could be modified with a numeric repeat value or with an asterisk (*):

P;999: print next 999 lines from the current position

P;*: print all lines from the current position to the end of file

F;999: move forward 999 lines from the current position

F;*: move to the end of file

B;999: move backward 999 lines from the current position

B;*: move to the first line of the file

Commands can be further modified with a line matching string or expression:

F:/xxx/;999 move forward to the line beginning with 999th occurrence of /xxx/

B:/xxx/;999 move backward to the line beginning with 999th occurrence of /xxx/

I:/xxx/;999:/yyy/ insert line yyy before the next 999 lines beginning with /xxx/

R:/xxx/;999;/yyy/ replace the next 999 lines beginning with /xxx/ with the line /yyy/

D:/xxx/;999 delete the next 999 lines beginning with /xxx/

For string mode, an S was added. Whenever /xxx/ was found within the line then the editwas applied:

FS:/xxx/;999 move forward to the 999th occurrence of the string /xxx/

IS:/xxx/;999:/yyy/ insert the string /yyy/ before the next 999 occurrences of /xxx/

RS:/xxx/;999:/yyy/ replace the next 999 occurrences of the string /xxx/ with /yyy/

DS:/xxx/;999 delete the next 999 occurrences of the string /xxx/

Lastly, the commands can be further modified with V to turn on verify mode and with O to specify nth occurrence string mode:

RVO:/xxx/;99;999:/yyy/ replace the 999th occurrence of string /xxx/ with /yyy/ and repeat it 99 times

There are a few other lesser used editing commands:

mark - to include files within files when the .mark <filename> statement is found in the current or subsequently included files (recursive operation)

befl - insert before the current line (normally the "A" command was used to insert after the current line)

trul <col> - truncate left most columns of the current file

trur <col> - truncate right most columns of the current file

In all edit command formats, the /xxx/ or /yyy/ or 999 could be replaced with a TEX variable.In addition, the 999 value could be replaced with an asterisk (*) to denote all occurrences.

TEX commands

TEX did not provide commands for numeric or conditional looping or switch cases as is common in modern scripting languages. These had to be constructed using if, labels and goto commands. As an example to eliminate duplicate lines from a file, we would use:

if <expression> - if conditional, the expression is of the form <variable|value>:op:<variable|value> where the op is one of the comparator ops mentioned earlier.

in:<expression> - print the expression and wait for input. Store input in the *in variable

int:<expression> - print the expression and wait for input specifically from the terminal. Store the input in the *in variable.

*null - no-input carriage return from the terminal, used to terminate insert mode in a TEX program. No other commands may be on the same line.

stop - stop the TEX program

_ - remarks line

return - return from a subroutine call

out:<expression> - print the expression to the terminal

outt:<expression> - force print the expression (and all prior output not yet flushed) to the terminal

scan:<operand-a>:<operand-b> - scan <operand-a> from left to right searching for <operand-b> and parse <operand-a> placing the results in *left, *middle, and *right star variables and if *match is T then a match was found.

scann:<operand-a>:<operand-b> - scan <operand-a> from left to right searching for <operand-b> and parse <operand-a> placing the results in *left, *middle, and *right star variables and if *match is T then a match was found. scann <operand-b> was limited to a single character or character class (*lc=lowercase alphabetic, *uc=uppercase alphabetic, *n=numeric, *a=alphabetic(*lc+*uc), *an=alphanumeric(*a+*n))

scanr:<operand-a>:<operand-b> - scan <operand-a> from right to left searching for <operand-b> and parse <operand-a> placing the results in *left, *middle, and *right star variables and if *match is T then a match was found.

scannr:<operand-a>:<operand-b> - scan <operand-a> from right to left searching for <operand-b> and parse <operand-a> placing the results in *left, *middle, and *right star variables and if *match is T then a match was found. scannr <operand-b> was limited to a single character or character class (*lc=lowercase alphabetic, *uc=uppercase alphabetic, *n=numeric, *a=alphabetic(*lc+*uc), *an=alphanumeric(*a+*n))

split:<operand-a>:<operand-b> - split <operand-a> at position <operand-b> starting from the beginning of <operand-a> placing the results in *left, *middle, and *right star variables

splitr:<operand-a>:<operand-b> - split <operand-a> at position <operand-b> starting from the end of <operand-a> placing the results in *left, *middle, and *right star variables

subs <subs_character> - activate subs mode where TEX will scan for pairs of <subs_characters>, evaluating the expression and placing it in the line prior to executing the line. SUBS mode is turned off by NOSUBS

trace - activate trace mode where lines are displayed prior to being executed. Trace mode is turned off by NOTRACE

vari - display all variables and their values including the star variables

TEX modes

TEX modes defined how other TEX commands would operate. The *svmd variable contained the current state of all TEX modes in the form of TEX commands to restore the modes. Each mode had an inverse command to turn the mode off which could be done at any time.

subs <char> / nosubs - activate subs mode where TEX will scan for pairs of <char>, evaluating the expression and placing it in the line prior to executing the line.

TSS commands

While beyond the scope of this article, the most commonly used TSS commands were:

NEW - new file (ie empty file / clears editor workspace)

OLD - old file brought into editor workspace

SAVE - save a new file (filename can't exist)

RESAVE - resave editor wokspace into an existing file

Example code

This code was excerpted from a TEX based Adventure game written by a team of Explorer Scouts from GE Post 635, Schenectady New York circa 1980. The Adventure game was the first of several popular online text-based adventure games available on the GE Timesharing service. The scouts decided to create their own adventure game using TEX. The original Adventure game used two word commands to navigate Colossal Cave. The parser shown below handled simple two word commands like go west or move right and converted them into x,y deltas for positioning and directional orientation in the game.

Notable features

The most notable feature in TEX was its SUBS mode allowing variable values to crossover and become executable code. It allowed a programmer to create new variables on the fly to be used in later TEX expressions in a LISP-like fashion. TEX also allowed programmers to create scripts on the fly via line editing, saving the content to file later to be executed as part of the current program using interfile call and goto statements. However, in most cases, these features were used to provide simple dynamic goto statements in code as seen in the Adventure game parser example. What other kinds of Artificial Intelligence constructs could be developed were never fully explored.

An example of creating variables on the fly and then using them to do an interfile goto.

_ next we modify mycat/mypgm_1_2 to say "hello world" we are writing some code to execute later in our script
old mycat/mypgm_1_2
r:*cl:/!label_3 out:'Hello World'/
resave mycat/mypgm_1_2

_ lastly we subs in x,y,z and then evaluate the goto mypgm_1_2!label_3 which does an interfile goto
goto mycat/mypgm_?x?_?y?!label_?z?

The TEX program above illustrates dynamic script creation and then execution via substitution, file editing and interfile gotos. In effect, programs writing programs were possible although seldom done. In the above example, the mycat/mypgm_1_2 file would be executed at label_3 printing out "hello world".